Process for preparing organohalosilanes

ABSTRACT

Organohalosilanes are prepared by the Rochow process of reacting metallic silicon particles with an organohalide in the presence of a copper catalyst. The metallic silicon particles, which are prepared by committing fragments of metallic silicon raw material, have a mean particle size of 10 mum to 10 mm and a surface oxygen quantity of at least 0.05 wt % and/or at least 0.001 g of oxygen/m2 of silicon surface area, which is given as the difference between the oxygen concentrations determined by in-metal oxygen analysis of the metallic silicon particles and the fragments, respectively. On analysis, the metallic silicon particles have been held for at least 3 hours in an air atmosphere at 25° C. and RH 55%

This invention relates to a process for preparing organohalosilanes bythe so-called Rochow reaction.

BACKGROUND OF THE INVENTION

The Rochow reaction is typically employed in the industrial process forthe synthesis of organohalosilanes such as methylchlorosilanes. TheRochow reaction is the direct reaction of organic halides such as alkylhalides and phenyl halides with metallic silicon particles which iscarried out at 250 to 500° C. in the presence of a copper catalyst and aco-catalyst. While this reaction requires keeping a high reaction rate,a key technology in the synthesis of methylchlorosilanes is to increasethe selectivity of the most desirable dimethyldichlorosilane. A keytechnology in the synthesis of phenylsilanes is to produce the desirablediphenyldichlorosilane and phenyltrichlorosilane in a compositionmatching with their demand.

The conventional Rochow reaction requires a very long time foractivation until the reaction reaches a steady state. The steady state,in turn, is relatively short. The contact mass's activity lowers withthe lapse of time, and the yield of diorganodichlorosilane decreasesaccordingly. In the synthesis of methylsilanes, for example, there ariseproblems that high-boiling fractions such as disilanes and undesiredproducts such as methyltrichlorosilane increase due to side reaction.This necessitates exchanging the contact mass in the reactor. Shorteningthe activation time is one of the outstanding problems. Since the Rochowreaction mainly uses reaction in a fluidized bed or agitating fluidizedbed, a variety of reports have been made on the particle size ofmetallic silicon particles suitable to form the fluidized bed.

In this reaction, it is important to increase the reaction rate ofmetallic silicon because the cost of metallic silicon is predominantamong the raw material cost. Since a variety of by-products usually formin addition to the desired diorganodichlorosilane, it is also importantto control reaction conditions so that the proportion of theseby-products may comply with the supply/demand balance oforganochlorosilanes. Industrially, this reaction is generally carriedout in a reactor such as a fluidized bed, vibrating fluidized bed oragitating fluidized bed while replenishing the contact mass to thereaction system. The reaction is a very complex gas-solid heterogeneousreaction in that the reaction itself occurs on surfaces of metallicsilicon particles and the catalyst is solid. For this reason, thereaction mechanism has not been well understood. It is empirically knownthat the results of reaction vary over a wide range depending on theattributes (including source, manufacturer, manufacturing equipment, andcrushing technique) of particular metallic silicon particles used.Several proposals have been made in this regard, but none of them havebecome established. In the present status, when metallic silicon of anew lot or origin becomes available, a preliminary reaction test must bedone to determine whether or not it can be used in practice. Since manyfactors of metallic silicon that affect the reaction have not yet beenrevealed, lively discussions have recently been made in the society ofmetallic silicon (see, for example, Silicon for the Chemical IndustryIV: Geirenger, Norway, Jun. 3-5, 1998).

What is important is the reaction activity of metallic silicon particlessubject to reaction. The reaction activity has been studied from variousaspects. In this regard, a variety of proposals (for example, relatingto properties of metallic silicon itself) have been made. Morespecifically, it is well known that aluminum which is present inmetallic silicon as an impurity is effective as a co-catalyst for theRochow reaction. Aluminum at the same level is active in some form, butinactive in other form. For the reason that only the active form ofaluminum present in metallic silicon as an impurity is necessary, H. M.Rong et al. reported the method of measuring active aluminum andrecommended the use of active aluminum (see Proceeding Silicon for theChemical Industry, pp. 69 (1998)). U.S. Pat. No. 5,334,738 or JP-A6-234776 discloses a method for quantitatively determining thedispersion of intermetallic compounds in metallic silicon as an impurityand the criterion of choice of metallic silicon for reactivity control.This method involves cutting a metallic silicon mass, polishing thesurface to a mirror finish, observing the morphology of the surfaceunder a microscope, and computing a structural parameter QF fromstructural factors. Metallic silicon having the structural parameter QFof 18 to 60 has the highest reactivity and its use is recommended. U.S.Pat. No. 5,281,739 discloses to evaluate the reactivity of a contactmass by adding copper to molten metallic silicon.

Making follow-up tests on these methods, we found that the reactivity ofmetallic silicon could not be determined by any of these methods whilethese methods were effective only in special limited systems. Thesemethods cannot be universally adopted.

In general, metallic silicon remains stable in that it has been oxidizedon its surface and is covered with stable silicon oxide so that inwardoxidation may not proceed beyond a certain thickness. However, as seenfrom the semiconductor silicon, it is well known that silicon itself hasa very high oxidizing ability and there is not available metallicsilicon which is free of oxide film in air. It is also known that thesurface of metallic silicon particles for use in the Rochow reaction hasmore or less oxide film, which affects the Rochow reaction. The oxidefilm on metallic silicon relative to reactivity and selectivity inmethylsilane reaction is discussed in the reports of G. J. Hutching etal., Silicon for the Chemical Industry, Geirenger, Norway, pp. 85-98,1992, and G. Laroze, Silicon for the Chemical Industry II, Leon, Norway,pp. 121-127, 1994. These reports describe the influence of oxide film onreactivity and selectivity while the oxide film on metallic siliconparticles is locally analyzed by x-ray photoelectron spectroscopy. Noreference is made to the activity of metallic silicon itself. Also, J.L. Falconer et al., J. Catal., vol. 159, pp. 31-41, 1996, study an oxidefilm on a silicon wafer and discuss the orientation of crystals andreactivity. This discussion is not applicable to the surface of metallicsilicon particles for the Rochow reaction, and no reference is made tothe activity of metallic silicon itself. None of the foregoing reportsestablish a measurement method for specifying metallic silicon particlesfor industrial use.

As understood from the above, the heretofore proposed methods are notgenerally applicable to the industrial use. When the Rochow reaction wasactually carried out using metallic silicon particles which wereselected under any of the foregoing selection criteria while theremaining factors are set identical, the results of reaction experienceda wide range of variation. Therefore, metallic silicon particles havingproperties specified by any of the prior art proposals are applicable toonly a special reaction system. There is a need to have metallic siliconparticles capable of finding practical use in the industry and theirevaluation method.

SUMMARY OF THE INVENTION

An object of the invention is to provide a process for preparingorganohalosilanes, capable of facilitating and ensuring the selection ofactive metallic silicon particles used in the Rochow reaction.

We have found that the activity of metallic silicon particles used inthe Rochow reaction is closely correlated to the thickness and quantityof oxide film formed on metallic silicon surface which can be measuredas a surface oxygen quantity. For the measurement of the surface oxygenquantity, metallic silicon particles and fragments of metallic siliconraw material which are to be comminuted into the metallic siliconparticles are separately measured for oxygen concentration by in-metaloxygen analysis (oxygen fractionation using an inert gas fusionfurnace), the surface oxygen quantity being given by the differencebetween these oxygen concentrations. The metallic silicon particlessubject to the measurement must be those which have been held for atleast 3 hours in an air atmosphere at 25° C. and RH 55% aftercomminution. This holding period ensures the accurate measurement of theactivity of metallic silicon particles. Metallic silicon particleshaving a surface oxygen quantity thus determined to be at least 0.05% byweight and/or at least 0.001 g of oxygen per square meter of siliconsurface area are selected for use in the reaction. This method ensuresto select metallic silicon particles having a high activity necessaryfor the synthesis of organohalosilanes by the direction reaction oforganic halides with metallic silicon powder. This enables to reduce theactivation time of the contact mass taken until the steady state isreached, also known as the triggering of reaction, which has been abottle neck in the Rochow reaction, improve the selectivity in thesteady state even when the rate of reaction is increased, and as aresult, increase the percent effective utilization of silicon. In oneprior art procedure relating to metallic silicon, a preliminary reactiontest using comminuted metallic silicon particles is performed forevaluating the reaction activity thereof before the industrial use ofmetallic silicon particles is decided. The present invention solves theproblem of such an extra test.

The invention provides a process for preparing organohalosilanescomprising reacting metallic silicon particles with an organohalide inthe presence of a copper catalyst. The metallic silicon particles, whichare prepared by comminuting fragments of metallic silicon raw material,have a mean particle size of 10 μm to 10 mm and a surface oxygenquantity of at least 0.05% by weight and/or at least 0.001 g of oxygenper square meter of silicon surface area, which is given as thedifference between the oxygen concentrations determined by in-metaloxygen analysis of the metallic silicon particles which have been heldfor at least 3 hours in an air atmosphere at 25° C. and RH 55% and thefragments, respectively.

In the prior art relating to the organochlorosilane synthesizingreaction (known as the Rochow reaction) between an alkyl halide (e.g.,methyl chloride) or aryl halide (e.g., benzene chloride) and metallicsilicon in the presence of a copper catalyst and co-catalyst, theoutstanding problems are the activation time (or induction period) takenlong until the steady state is reached as well as the reaction rate andselectivity to form silanes. To solve these problems, an improvement incatalyst composition and an improvement in metallic silicon particlesthemselves are necessary. We have learned the mechanism of silanereaction and succeeded in consistently optimizing metallic siliconparticles, thereby solving the above-mentioned problems of the Rochowreaction. It becomes possible to increase the selectivity of the desireddiorganodihalosilane and improve the yields of reaction products. Italso becomes possible to exclude the preliminary reaction test sufferingfrom a wide range of variation and manage the Rochow reaction in aquantitative manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The only FIGURE, FIG. 1 schematically illustrates a system for thepreparation of organohalosilanes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is directed to a process of contacting an organohalide(e.g., alkyl halide or aryl halide) with metallic silicon particles inthe presence of a copper catalyst to form organohalosilanes of thefollowing formula:

R_(m)H_(n)SiX_(4−m−n)  (1)

wherein R is C₁₋₄ alkyl or aryl such as phenyl, X is a halogen atom suchas chlorine or bromine, and “m” is an integer of 1, 2 or 3, “n” is aninteger of 0, 1 or 2, and m+n is an integer of 1, 2 or 3. In particular,the invention places a focus on the metallic silicon particles used inthis Rochow reaction. Therefore, the invention pertains to the selectionof metallic silicon particles which can reduce the activation time (orinduction period) taken until the reaction reaches a steady state, thathas been a bottle neck in reaction of this sort, and sustain the highactivity in the steady state, to the method of evaluating the activityfor enabling that selection, and to the use of metallic siliconparticles in the Rochow reaction.

More particularly, metallic silicon is usually prepared by reducingsilica along with carbon in an arc furnace at a high temperature above2,500° C., which requires a large amount of electric energy andnaturally adds to the cost of silicon. The cost of organohalosilanewhich is a precursor to silicone resin largely depends on the conversionrate of the expensive metallic silicon to the silane (because a varietyof silane by-products form due to side reaction), the production rate(or selectivity) of useful silanes meeting the demand balance, and thereaction rate which is considered important for the industrial process.From such a standpoint, silicone manufacturers use the simple term“reactivity” for both the selectivity and reaction rate of the productand seek for metallic silicon capable of exhibiting a high reactivity intheir own manufacturing apparatus. On the other hand, regarding metallicsilicon for use in the Rochow reaction and the manufacture oftrichlorosilane as a semiconductor raw material approximate to theRochow reaction (the majority of the overall consumption of metallicsilicon is used in these industrial areas), metallic siliconmanufacturers actually perform a simulation of the reaction and makefrom their own aspect research for forming metallic silicon having ahigh reactivity and selectivity while paying attention to the contentand form of impurities, manufacturing method, cooling method, etc. Thefruitful results of such research about metallic silicon for chemicaluse are reported in the international meeting “Silicon for ChemicalIndustry” held in Norway at intervals of every two years whereinformation exchange is made. Since the Rochow reaction itself is notthoroughly understood up to the present, each manufacturer makes theevaluation of metallic silicon based on its own scale.

The Rochow reaction is a gas-solid heterogeneous reaction between theorganic halide which is gaseous at elevated temperature and metallicsilicon which is solid even at elevated temperature in the presence of acatalyst. Since it is expected that the reactivity largely depends onthe nature of metallic silicon as crystal, the method for quantitativelydetermining the dispersion of intermetallic compounds as impurities inmetallic silicon and the criterion of choosing metallic silicon forreactivity control proposed in JP-A 6-234776 are reasonable at a glanceand worth considering. This method involves cutting a metallic siliconmass, polishing the surface to a mirror finish, observing themetallurgical state of the surface under a microscope, and computing astructural parameter QF from structural factors. The use of metallicsilicon having the structural parameter QF of 18 to 60 is recommendedbecause of the highest reactivity.

However, making analysis on the size of crystallites in ordinarymetallic silicon of industrial grade, we found that crystallites inordinary metallic silicon of industrial grade are of millimeter orderbecause silicon is highly crystalline. By contrast, metallic siliconparticles used in actual reaction have a size of about 100 microns atmost. It is then evident that metallic silicon particles used in theRochow reaction each consist of a few crystallites. It is thus believedthat the state of intermetallic compounds in metallic silicon asimpurities observed under a microscope does not always represent thecrystallinity of metallic silicon that governs reactivity.

Since crystal defects are present in these zones, comminution ofmetallic silicon causes impurity-containing areas to selectively developat surfaces. The active aluminum theory proposed by H. M. Rong et al.,Proceeding Silicon for the Chemical Industry, pp. 69, 1998, isconsidered, based on its measurement method (measured in terms of thequantity extracted with aqueous hydrochloric acid), to indicate thataluminum present on surfaces of metallic silicon particles is active.However, these areas selectively develop at surfaces as a result ofcomminution, the extracted quantity is proportional to the amount ofaluminum, and the percent extraction is substantially constant. Themethod of H. M. Rong et al. cannot be directly applied to the relevantreaction.

As described above, the Rochow reaction is a gas-solid heterogeneousreaction between the organic halide which is gaseous at elevatedtemperature and metallic silicon particles which remain solid even atelevated temperature. As understood from the reports of G. Laroze,Silicon for the Chemical Industry II, Leon, Norway, pp. 121-127, 1994and J. L. Falconer et al., J. Catal., vol. 159, pp. 31-41, 1996, it isfully anticipated that reactivity is largely affected by the crystalorientation of metallic silicon particles and the surface state of oxidefilm, etc. However, a precise study of the Falconer report reveals thatonly the oxide film on metallic silicon and the selectivity inmethylsilane reaction are discussed using semiconductor silicon. Thistheory is applicable with difficulty to metallic silicon particles foractual use in the industry. In the Laroze report, a specific measurementmethod is not referred to.

Since silicon is highly reactive in air, an oxide film forms on thesurface of metallic silicon as a result of contact with air. In general,comminution, transportation and storage of metallic silicon mass areperformed in an inert gas or in an atmosphere having a low oxygenconcentration in order to avoid the danger of dust explosion. Sinceoxygen is not always completely shielded, an oxide film normally existson the surface of metallic silicon. It is also empirically known thatthe reactivity of metallic silicon differs with storage conditions.

On the other hand, the process of manufacturing metallic silicon forindustrial use involves, for the purpose of reducing impurities such asaluminum and calcium, the refining step of tapping silicon material intoa tapping container known as ladle, and blowing oxygen or air into themolten silicon material from below, to convert the impurities intooxides for removal. In this step, silicon is also somewhat oxidized.Since the silicon monoxide thus formed has a high vapor pressure andsilicon is highly crystalline as previously mentioned, silicon oxide(including silicon monoxide and dioxide) is excluded as slag uponcooling entailing crystal growth. Then little oxygen is present inmetallic silicon.

It has thus been found that the majority of oxygen measured by oxygenanalysis on metallic silicon particles in an inert gas fusion furnace isattributable to oxygen present on surfaces thereof. Since fineparticulates of slag can, of course, be internally included depending onthe manufacturing process, the absence of such slag particulates must beconfirmed before analysis.

Through the foregoing investigations, we have found that provided thatmetallic silicon particles are prepared by comminuting fragments ofmetallic silicon raw material, the quantity of surface oxygen onmetallic silicon particles is represented by the difference between theoxygen quantities of the metallic silicon particles and the fragmentswhich are measured by means of an inert gas fusion furnace-built-inoxygen analyzer (generally known as an in-metal oxygen analyzer andcommercially available as model EMGA-650 from Horiba Ltd.). We havefurther found that the surface oxygen quantity is divided by the surfacearea of metallic silicon particles to calculate an oxygen quantity perunit surface area, which becomes a useful parameter. The metallicsilicon particles subject to the measurement must be those which havebeen held for at least 3 hours in an air atmosphere at 25° C. and RH 55%after comminution. Since the surface oxidation of metallic siliconparticles is substantially saturated within about 3 hours, the upperlimit of the holding time is not particularly limited. The time ofholding in air is preferably 3 to 48 hours, and more preferably 16 to 24hours.

As mentioned above, metallic silicon particles are highly oxidative sothat the surface is oxidized by bonding with oxygen in air. The degreeof surface oxidation largely varies with the storage environment andtime. Therefore, in carrying out in-metal oxygen analysis on metallicsilicon particles for determining a “surface oxygen quantity,” the valueof in-metal oxygen analysis changes depending on the storage conditionsunder which the metallic silicon particles have been stored. In order toensure that the activity of metallic silicon particles in Rochowreaction is determined, oxygen analysis must be effected on the metallicsilicon particles which have been held for at least 3 hours, preferably3 to 48 hours, and more preferably 16 to 24 hours in an air atmosphereat 25° C. and RH 55%. Such metallic silicon particles subject tomeasurement are obtained by comminuting metallic silicon fragments(obtained by crushing a metallic silicon mass) in an inert gas stream ora low oxygen concentration (typically, 15% or less) atmosphere to aparticle size suitable for Rochow reaction, specifically a mean particlesize of 10 μm to 10 mm, and immediately thereafter, holding the metallicsilicon particles for at least 3 hours, preferably 16 to 24 hours in anair atmosphere at 25° C. and RH 55%. The respective steps of thein-metal oxygen analysis on the thus prepared (or conditioned) metallicsilicon particles, including sampling, handling, and placement in theinstrument need not avoid contact with air. That is, the analysis may bemade in any desired environment.

The other sample subject to oxygen analysis is fragments of metallicsilicon raw material which are obtained by crushing a metallic siliconmass into fragments, and collecting fragments with a weight of 20 to 100mg, which are measured for oxygen quantity without treatment. Since thesurface area of metallic silicon fragments is negligibly small ascompared with comminuted powder, the contact thereof with oxygen neednot be controlled.

By computing the difference between the oxygen quantities of themetallic silicon particles and the fragments, the quantity of surfaceoxygen on metallic silicon particles which are actually subject to theRochow reaction is determined.

The feature of the present invention is to select metallic siliconparticles by measuring the quantity of oxide film on surfaces ofmetallic silicon particles. Comparing the surface oxygen quantities onvarious metallic silicon specimens, we have found that metallic siliconparticles having a surface oxygen quantity of at least 0.05% by weight,preferably at least 0.1% by weight, and/or at least 0.001 g per squaremeter of silicon surface area, preferably at least 0.002 g per squaremeter of silicon surface area as measured by the above-specifiedprocedure especially have an excellent activity. Differently stated, theprocedure involving separately measuring the oxygen quantities presenton metallic silicon particles which have been held for at least 3 hoursin an air atmosphere at 25° C. and RH 55% and fragments as their sourceby in-metal oxygen analysis (oxygen analysis in an inert gas fusionfurnace) and computing the difference therebetween to give the surfaceoxygen quantity is appropriate for the evaluation of metallic siliconparticles. This eliminates a need for a preliminary reaction test onmetallic silicon particles and enables quantitative management of thereaction.

As the surface oxygen quantity of the metallic silicon particles becomeshigher, the activity becomes higher. However, on the selection ofmetallic silicon particles, the surface oxygen quantity is usually up to1.0% by weight, and especially up to 0.5% by weight.

The metallic silicon particles actually used in the preparation oforganohalosilanes should have a mean particle size of 10 μm to 10 mm andsatisfy the above criterion of selection and should preferably have beenstored in a surface non-oxidized state (that is, stored in aircontactavoiding conditions, typically in a nitrogen gas atmosphere). Asthe more preferred criterion for selecting metallic silicon particles,the metallic silicon particles should have a taken-up oxygen quantity ofup to 0.3% by weight, further preferably up to 0.25% by weight, and mostpreferably up to 0.2% by weight, which is given as the differencebetween the oxygen concentrations determined by in-metal oxygen analysisof the metallic silicon particles stored in a surface non-oxidized state(to be actually used in the reaction) and the fragments (from which theparticles are obtained by comminution), respectively. Alternatively, themetallic silicon particles actually used should contain up to 0.01 g ofoxygen per m² of silicon surface area, further preferably up to 0.005 gof oxygen/² of silicon surface area, and most preferably less than 0.003g of oxygen/m² of silicon surface area, provided that the oxygenquantity is similarly determined.

Excepting the use of the above-defined metallic silicon particles, theorganohalosilane preparing process of the invention may be carried outby employing any well-known procedure and conditions. For example, thecopper catalyst and co-catalyst may be selected from well-known ones.The organic halide used may be selected from alkyl halides and arylhalides having an alkyl or aryl group corresponding to a desiredorganohalosilane, for example, methyl chloride, ethyl chloride, andphenyl chloride. According to the invention, organohalosilanes of theabove formula (1), especially diorganodihalosilanes wherein m=2 and n=0,can be produced in high yields.

The amount of the copper catalyst added may be about 0.1 to about 10parts by weight per 100 parts by weight of the metallic silicon. Any ofwell-known co-catalysts may be added to the copper catalyst.

FIG. 1 illustrates a system for preparing organohalosilanes. The systemincludes a fluidized bed reactor 1 and a reactant source tank 3connected to the bottom of the reactor 1 through a reactant feed conduit2, whereby metallic silicon and a copper catalyst or a mixture of acopper catalyst and a co-catalyst are admitted into the bottom of thereactor 1. A conduit 4 for the other reactant, organic halide has aheater 5 inserted therein and is connected to the reactor 1 at thebottom. The organic halide in gas or vapor form is also introduced intothe bottom of the reactor 1, thereby forming a fluidized bed 1 a of themetallic silicon and the catalyst within the reactor 1. The reactor 1 isenclosed with a cooling jacket 6.

Preferably the organic halide in gas or vapor form is introduced intothe reactor 1 at a linear velocity of 2 to 10 cm/sec in the steadystate. Reaction is generally carried out at a temperature of 250 to 350°C.

The organohalosilane product resulting from the reaction is channeledthrough a discharge conduit 7 connected to the top of the reactor 1 to afirst cyclone 8 where the entrained solid particles are separated andfed back to the fluidized bed la through a return pipe 9. The product isthen fed to a second cyclone 10 where the entrained solid particles areseparated and fed to a particle reservoir 11 for storage. The product isthen fed to first and second silane condensers 12 and 13 where theorganohalosilanes are condensed and fed to a silane reservoir 14 forstorage. Part or all of the discharge gas from which solid particleshave been separated and organohalosilanes have been condensed andseparated is fed back to the reactor 1 through an organic halide returnconduit 16 having a recycle gas compressor 15 inserted herein. Thereturn conduit 16 is connected to the organic halide feed conduit 4.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. All parts are by weight.

Using a system as shown in FIG. 1, methylchlorosilanes were prepared. Asteel reactor of 8 cm in diameter equipped with a spiral agitator andthoroughly purged with nitrogen was charged with 100 parts of each ofmetallic silicon powders of different produces having a mean particlesize of about 50 μm which had been stored in an inert atmosphere aftercomminution as shown in Table 1. With stirring by the spiral agitator,nitrogen gas was introduced into the reactor at a linear velocity of 2cm/sec to fluidize the silicon powder while the powder was heated to280° C. Thereafter, 3 parts of a catalyst mixture was added to thereactor. The catalyst mixture consisted of a copper catalyst in the formof a flake copper foil powder obtained by stamping, having anair-permeability method specific surface area of 0.80 m²/g, a meanparticle size of 47 μm, and a bulk specific gravity of 1.9 g/cm³ and aco-catalyst composed mainly of antimony, brass and bronze. While thereaction temperature was controlled in the range of 280 to 300° C.,methyl chloride was slowly introduced into the reactor for reaction. Themethyl chloride feed was ultimately increased to a linear velocity of 7cm/sec, at which reaction was continued. After 6 hours, the reaction wasstopped. The average rate of silane production and the composition ofthe formed silanes are shown in Table 2.

TABLE 1 Oxygen in BET powder** Activity* Activity* specific Oxygen in(taken-up (surface (surface Metallic Fe Al Ca surface fragments oxygen)oxygen) oxygen) silicon (%) (%) (%) area (m²/g) *** (wt %) (wt %) (wt %)(g/m²) No. 1 0.15 0.06 0.02 0.06 <0.01 0.03 0.15 0.0025 No. 2 0.24 0.160.01 0.58 <0.01 0.03 0.10 0.0017 No. 3 0.20 0.05 0.05 0.65 <0.01 0.060.19 0.0026 No. 4 0.32 0.16 0.05 0.53 <0.01 0.04 0.23 0.0043 No. 5 0.290.05 0.03 0.64 <0.01 0.05 0.19 0.0030 No. 6 0.25 0.09 0.03 0.60 <0.010.06 0.24 0.0040 *Activity was measured by in-metal oxygen analysis(oxygen fractionation using an inert gas fusion furnace) after metallicsilicon particles were held for 24 hours in air at 25° C. and RH 55%.**Powder was stored in an inert atmosphere and used in the reaction.***Oxygen in fragments was measured by similar in-metal oxygen anaylsison fragments of metallic silicon raw material.

* Activity was measured by in-metal oxygen analysis (oxygenfractionation using an inert gas fusion furnace) after metallic siliconparticles were held for 24 hours in air at 25° C. and RH 55%.

** Powder was stored in an inert atmosphere and used in the reaction.

*** Oxygen in fragments was measured by similar inmetal oxygen analysison fragments of metallic silicon raw material.

TABLE 2 Activity* Silane (surface production MeSiCl₃/ Metallic oxygen)rate (g/100 Me(H)SiCl₂ Me₂SiCl₂ Me₂SiCl₂ silicon (wt %) g- Si · hr) (%)(%) ratio No. 1 0.15 22.1 1.4 89.0 0.055 No. 2 0.10 21.5 1.8 86.3 0.059No. 3 0.19 25.1 1.3 91.2 0.048 No. 4 0.23 28.5 1.2 93.1 0.045 No. 5 0.1923.2 1.5 91.4 0.042 No. 6 0.24 33.8 1.2 93.8 0.040

There have been described metallic silicon particles with a specificparameter which are active in the Rochow reaction, effective inincreasing the reaction rate, especially in the activation period, andreducing the activation period, and eventually improving the results ofthe Rochow reaction. The invention eliminates a need for a preliminaryreaction test on metallic silicon whose results have a wide range ofvariation, and enables a quantitative forecast of the activity ofmetallic silicon particles. The invention is valuable and epoch-makingin the industry in that the selection of metallic silicon particlesoptimum for the Rochow reaction is possible.

Japanese Patent Application No. 11-142922 is incorporated herein byreference.

Reasonable modifications and variations are possible from the foregoingdisclosure without departing from either the spirit or scope of thepresent invention as defined by the claims.

What is claimed is:
 1. A process for preparing organohalosilanescomprising reacting metallic silicon particles having a mean particlesize of 10 μm to 10 mm with an organohalide in the presence of a coppercatalyst, wherein the metallic silicon particles, which are prepared bycomminuting fragments of metallic silicon raw material, have a surfaceoxygen quantity of at least 0.05 wt % and/or at least 0.001 g of oxygenper square meter of silicon surface area, which is given as thedifference between the oxygen concentrations determined by in-metaloxygen analysis of the metallic silicon particles which have been heldfor at least 3 hours in an air atmosphere at 25° C. and RH 55% and thefragments, respectively.
 2. The process of claim 1 wherein the metallicsilicon particles have a taken-up oxygen quantity of up to 0.3 wt %. 3.The process of claim 1, wherein the metallic silicon particles are heldin the air atmosphere for 3 to 48 hours.
 4. The process of claim 3,wherein the metallic silicon particles are held in the air atmospherefor 16 to 24 hours.
 5. The process of claim 1, wherein the metallicsilicon particles have a surface oxygen quantity of at least 0.1% byweight.
 6. The process of claim 1, wherein the metallic siliconparticles have a surface oxygen quantity of at least 0.002 g per squaremeter of silicon surface area.
 7. The process of claim 1, wherein themetallic silicon particles have a surface oxygen quantity of up to 0.2%by weight.
 8. The process of claim 1, wherein the metallic siliconparticles have a surface oxygen quantity of up to 0.25% by weight. 9.The process of claim, 1, wherein the metallic silicon particles have asurface oxygen quantity of up to 0.5% by weight.
 10. The process ofclaim 1, wherein the metallic silicon particles have a surface oxygenquantity of up to 1.0% by weight.
 11. The process of claim 1, whereinthe metallic silicon particles have a surface oxygen quantity of up to0.01 g of oxygen per square meter of silicon surface area.
 12. Theprocess of claim 1, wherein the metallic silicon particles have asurface oxygen quantity of up to 0.005g of oxygen per square meter ofsilicon surface area.
 13. The process of claim 1, wherein the metallicsilicon particles have a surface oxygen quantity of less than 0.003 g ofoxygen per square meter of silicon surface area.
 14. The process ofclaim 1, wherein the organohalide is an alkyl halide or an aryl halide.15. The process of claim 1, wherein the organohalide is methyl chloride,ethyl chloride or phenyl chloride.
 16. The process of claim 1, whereinthe amount of the copper catalyst is 0.1 to 10 parts by weight per 100parts by weight of the metallic silicon.